For the rapid and effective diagnosis and treatment of infectious diseases, it is desirable to be able to detect the micororganism causing the disease as rapidly as possible. Infections of the urinary tract are among the most common bacterial diseases, second in frequency only to infections of the respiratory tract. Such urinary tract infections (UTI) are usually associated with bacterial counts of 100,000 or more organisms per mL of urine, a condition referred to as significant bacteriuria.
Current laboratory methods for the detection of significatn bacteriuria are based on culturing the sample suspected of containing the microorganism. However, these methods are time consuming and require considerable clinical training and facilities.
My co-workers at the laboratories of the assignee of the present invention found that the cells indicating significant bacteriuria could be separated from the urine sample and detected using sensitive redox reagents. It was found, however, that even after sterile urine had been filtered and washed with buffer, the redox reagents were sensitive enough to detect the small amount of residual reductant that was left behind from the urine. thus, even when urine samples that contained no infection were tested, significant background densities were obtained due to extraneous reductants present. In addition, background densities varied from patient to patient.
Urine samples contain a wide variety of potentially interfering reducing agents such as glutatione, cysteine, uric acid and ascorbic acid to mention but a few.
In the determination of substances other than cells in urine, it is common to add materials to the sample before testing in order to reduce the interference caused by reducing agents. In U.S. Pat. No. 3,411,877 issued Nov. 19, 1968, there is disclosed a treatment which comprises adding to the sample an ionizable heavy metal compound. The analyte (e.g. glucose) is then determined using an oxidase enzyme (e.g. glucose oxidase). In Japanese Kokai 58-55757 published Apr. 2, 1983, there is disclosed a urine treatment which comprises adding to the sample a metal chelating compound (e.g. iron(III)ethylenediaminetetraacetic acid [iron(III)EDTA]). Neither of these references is concerned with the problem of determining the presence of cells such as in the determination of significant bacteriuria. In both cases, the treating substance is present at the time the subsequent quantitating reaction takes place.
In the determination of cells, we have found that the treatment using iron(III)EDTA alone is not sufficient to remove all of the background due to reducing substances. For example, when sterile urine samples were washed with solutions containing only iron(III)EDTA, background was reduced somewhat but higher background densities than desired were obtained.